The present invention concerns a novel method to control certain insect pests, specifically those that have developed resistance to one or more classes of insecticides, through the use of N-substituted sulfoximines.
The development of resistance to insecticides in insect populations is a well recognized phenomenon and there are well documented cases of resistance for all of the major classes of insecticides (Georghiou and Saito, 1984 Pest Resistance to Pesticides. Plenum Press, New York; Whalon et al., 2007 Arthropod Pest Resistance Database, http://www.cips.msu.edu/resistance/rmdb). The reduction in effectiveness of insecticides due to the development of resistance is one of the forces that drives the discovery and development of new insecticides.
Predicting whether or not a resistance mechanism that has conferred resistance to an existing insecticide will confer resistance to a novel insecticide (i.e., cross-resistance) is not necessarily a simple matter. In the case where resistance is conferred by a change or modification in the molecular target at which the insecticide acts (i.e., target-site resistance), a novel insecticide that acts at a different target site is unlikely to be affected by the resistance mechanism. Thus, in such a case in which the target site at which a novel chemistry acts is known and the resistance mechanism of concern involves a modification to a different target site, one could predict with some confidence that the resistance mechanism would not confer resistance to the novel chemistry.
In contrast to the above, the case where the target site of the novel chemistry is not known or where resistance is conferred by some mechanism other than target site insensitivity (e.g., metabolic detoxification, sequestration, or excretion), cross resistance is difficult to predict. In these cases, empirical assessment of the cross-resistance among insecticide chemistries using well characterized resistant populations or “strains” of a target pest species provides the most direct and compelling evidence for the likelihood of cross-resistance
One of the newer and more successful classes of insecticides to be introduced in past 25 years is the neonicotinoids. The introduction of neonicotinoid insecticides has provided growers with invaluable new tools for managing some of the world's most destructive crop pests, including species with a long history of developing resistance to earlier-used products. Imidacloprid was the first major active ingredient of the neonicotinoid class to reach the market. Research on molecules with a similar structure containing the 6-chloro-3-pyridylmethyl moiety led to acetamiprid, nitenpyram and thiacloprid. The substitution of the chloropyridinyl moiety by a chlorothiazolyl group resulted in a second subgroup of neonicotinoid insecticides including clothianidin and thiamethoxam.
Although the neonicotinoids have proved relatively resilient to the development of resistance, high levels of resistance have been documented in field-collected populations of the whitefly, Bemisia tabaci. During the late 1990s, resistant species increased in potency with more recently-collected strains of this whitefly exhibiting more than 100-fold resistance to imidacloprid, and comparable levels of resistance to thiamethoxam and acetamiprid (Elbert and Nauen, 2000 Pest Manag Sci. 56: 60-64; Rauch and Nauen, 2003 Arch Insects Biochem Physiol. 54: 165-176; Gorman et al., 2003 Proc BCPC Intl Cong: Crop Science & Technology. 2: 783-788). The major mechanism of resistance in whitefly to neonicotinoid insecticides appears to be an elevated detoxification capability (Rauch and Nauen, 2003 Arch Insects Biochem Physiol. 54: 165-176) and no target-site resistance has been found in neonicotinoid-resistant whitefly populations (Nauen and Denholm, 2005 Arch Insect Biochem Physiol. 58:200-215).
Neonicotinoid insecticides remain valuable and effective tools for the management of insect pests in most areas in spite of the limited development of resistance. Control of neonicotinoid-resistant insect pest populations, or for that matter other insecticide-resistant insect pest populations, will rely on the availability of insecticides that are effective on the resistant populations. Preventing or delaying the development of insecticide-resistant insect pest populations also relies on the rotation of insecticides that are not affected by the same resistance mechanisms. In either case, new insecticides that lack cross-resistance to currently available insecticides are imminently needed.